106 THE ANTARCTIC MANUAL. 
The temperature of a saline solution at its freezing-point is raised 
by melting ice in it, and the rate at which it raises the temperature 
of the solution is the less the greater the amount of ice melted. The 
more nearly the temperature of the solution approaches to 0° C., the 
greater is the amount of ice which must be melted in order to pro- 
duce a certain rise of temperature. When the temperature of the 
solution is ever so little below 0° C., the amount of ice which has to 
be melted in order to produce the smallest rise of temperature is ever 
so great. But the temperature at which ice melts in a solution is 
the temperature at which the solution freezes. Therefore, for solu- 
‘ tions containing the same amount of a salt, the depression of the 
freezing-point is the less the greater the amount of water present. 
In some cases the depression of the freezing-point is exactly propor- 
tional to the reciprocal of the amount of water present; in other 
cases it deviates slightly from exact proportionality in one sense or 
in the other. 
The temperature of a solution at its boiling-point is lowered 
by condensing steam in it; and the rate at which it lowers the 
temperature of the solution is the less the greater the amount of 
steam condensed. The more nearly the temperature of the solution 
approaches the temperature at which saturated steam condenses on 
pure water, the greater is the amount of steam which must be con- 
densed in order to produce a certain fall of temperature. When the 
temperature of the solution is ever so little above the boiling-point 
of pure water, the amount of steam which has to be condensed in 
order to produce the smallest fall of temperature is ever so great. 
But the temperature at which steam condenses in a solution is the 
temperature at which the solution boils. Therefore, for solutions 
containing the same amount of a salt, the elevation of the boiling- 
point is the less the greater the amount of water present. In some 
cases the elevation of the boiling-point is exactly proportional to the 
reciprocal of the quantity of water present; in other cases it deviates 
slightly from exact proportionality in one sense or in the other. 
If T; be the freezing-point of water, and t, be the freezing-point 
of a solution which for a certain quantity of dissolved salt contains a 
quantity Wy; of water, then the value of the product Wy (Ty — ¢) 
is constant in the case of some salts; in the case of others it increases 
as Wy, or the amount of water, increases; in the case of others again 
it decreases as the dilution increases. But the deviations from con- 
stancy are never great even in nearly saturated solutions. 
If T, be the boiling-point of water, and t be the boiling-point of 
a solution which, for a certain quantity of dissolved salt, contains a 
